Re: Adding linux_link(2) system call

[Emmanuel Dreyfus <manu%netbsd.org@localhost>]

On Fri, Jul 29, 2011 at 11:37:48AM -0400, Greg Troxel wrote:
> >     a) Create a file A
> >     b) Create a symlink X->A
> >     c) Create a hard link Y=X
> >     d) Unlink a
> >     e) Create a directory A

Here is what happens. The semantics are really different.
$ touch A
$ ln -s A X
$ ln X Y
$ unlink A
$ mkdir A
$ ls -lid A X Y
1135709 drwxrwxr-x  2 manu manu 4096 jui 29 20:33 A
1135711 lrwxrwxrwx  2 manu manu    1 jui 29 20:33 X -> A
1135711 lrwxrwxrwx  2 manu manu    1 jui 29 20:33 Y -> A
$ uname
Linux

$ cd /tmp
$ touch A
$ ln -s A X
$ ln X Y
$ unlink A
$ mkdir A
$ ls -lid A X Y
672129 drwxr-xr-x  2 manu  wheel  512 Jul 29 20:35 A
533126 lrwxr-xr-x  1 manu  wheel    1 Jul 29 20:35 X -> A
533109 -rw-r--r--  1 manu  wheel    0 Jul 29 20:35 Y
$ uname
NetBSD

> >     a) Create a symlink X-A', where A' doesn't exist
> >     b) Create a hard link Y=X
> >     c) Create a directory A

$ ln -s A X
$ ln X Y
$ mkdir A
$ ls -lid A X Y
1135711 drwxrwxr-x  2 manu manu 4096 jui 29 20:38 A
1135709 lrwxrwxrwx  2 manu manu    1 jui 29 20:38 X -> A
1135709 lrwxrwxrwx  2 manu manu    1 jui 29 20:38 Y -> A
$ uname
Linux

$ rm -Rf A X Y
$ ln -s A X
$ ln X Y
ln: X: No such file or directory
$ uname
NetBSD

> Is there some way in Linux to change the symlink target and have both
> (hardlinked) source names point to the new target?

Here is my attempt:
$ touch A B
$ ln -s A X
$ ln X Y
$ ln -sf B X
$ ls -lid A B X Y
1135709 -rw-rw-r--  1 manu manu 0 jui 29 20:40 A
1135711 -rw-rw-r--  1 manu manu 0 jui 29 20:40 B
1135719 lrwxrwxrwx  1 manu manu 1 jui 29 20:41 X -> B
1135717 lrwxrwxrwx  1 manu manu 1 jui 29 20:40 Y -> A

-- 
Emmanuel Dreyfus
manu%netbsd.org@localhost